This invention relates to a plastic globe for use in lighting applications and a method of manufacturing the same.
Outdoor luminaires such as High Intensity Discharge (HID) lighting fixtures include an optical unit also called a xe2x80x9cglobexe2x80x9d which functions to protect the enclosed light source and redirect light in a manner desired by the lighting designer. Light redirection is typically accomplished by means of reflecting and/or refracting prisms disposed on inner and/or outer surfaces of the globe to reflect and refract light rays respectively. Such globes must, of course, be at least partially translucent and are therefore formed of glass or plastic.
Glass globes have heretofore been preferred by lighting designers because of their superior longevity and appearance. Greater longevity arises because glass typically has greater resistance to sunlight and inclement weather and is therefore less likely to discolor or xe2x80x9cyellowxe2x80x9d as a result of exposure. As a material, glass provides a superior appearance because of the phenomena known as xe2x80x9cglowxe2x80x9d or xe2x80x9csparklexe2x80x9d which arises from small amounts of light passing through textured surfaces and corners of prismatic structures disposed on the light emitting surfaces of the globe. As those skilled in the art will recognize, this phenomena is unique to glass and arises as a result of the manufacturing process specifically the prismatic structures are imparted with slight radii or xe2x80x9crounded cornersxe2x80x9d due to the high viscosity of the glass material during formation of the globe. The light emitting surfaces are further imparted with a surface texture due to xe2x80x9cheat checksxe2x80x9d or small fissures in the surface metal of the cast iron forming molds due to wear, polishing, and material build up.
Plastic, in contrast, becomes very fluid with a relatively low viscosity during the molding process. This allows very small details to be created and repeated during manufacturing. Accordingly, very sharp corners can be reproduced in prismatic structures Plastic parts are also typically injection molded using highly polished steel resulting in smooth surfaces on the plastic globe. In addition, the wear of the surfaces is minimal, thus maintaining the smooth surfaces. Accordingly, while plastic globes can be manufactured at substantially lower weight, with greater precision and with perhaps greater performance properties then glass, plastic has a noticeably different appearance.
Consequently a need exists for a plastic globe and a method of manufacturing the same which overcomes the above-mentioned difficulties resulting in a globe having an aesthetically pleasing appearance which emulates the xe2x80x9csparklexe2x80x9d or xe2x80x9cglowxe2x80x9d of glass, when in use.
It is the principal object of the present invention to provide a plastic globe for use in lighting applications which emulates the appearance of glass during operation of the corresponding lighting fixture.
In carrying out the above object, there is provided a method of manufacturing a plastic globe which.comprises imparting a surface texture, preferably a somewhat rough surface, to at least a portion of one surface of the globe. The texture is imparted by etching the globe itself and/or etching corresponding mold surfaces prior to forming the globe. The method may further comprise alone, or in combination with the above etching, forming a plurality of prisms on at least one surface of the globe With a plurality of the prisms each having a corner with at least one radius to permit light to leak through during use.
These and other objects, features, and advantages of the present invention will become more readily apparent by reference to the following description of the drawings wherein like reference numerals correspond to like components.